Changing physical damage calculations?

I think I understand. For each bit I want to check, I double the value of the number by the 89, starting with 01 (0 MP=Death), then on to 02, 03, 08, 10, 20, 40 and 80. So if I wanted to make the Man Eater weapon do double damage to undead enemies, I would change the BIT #$10 (checks for Human) into BIT#$80. I think I have the desired effect, here, because double damage to undead enemies is exactly what is happening. Thank you!